Sunday, November 17, 2013

Evolution in texbook

I saw some sentences in the chapter on genetics and evolution in Sujit's textbook which I think are not correct. I am commenting here on only some of them. I am sure a professional in the field will spot a lot more errors than I did. My frustration with the system of education prevalent here is that you have to write exactly as given in the textbook even if it is wrong. If sujit writes what I tell him, he will fail in the exam.“Why create a generation of thinkers when what’s needed are workers?” seems to be the thinking behind education in most Indian schools. I will start with the definition of evolution given in the textbook:

Evolution may be defined as a gradual development of more complex species from pre-existing simpler forms.

This definition is unhelpful. In biology, development refers to the changes in a single individual over its lifetime. Using this word confuses a basic idea: individuals don't evolve, populations do. Also, it is not necessary that evolution always results in production of greater complexity. For eg., the tapeworm lost its digestive system when it became an intestinal parasite. It has no need for one. The most successful organisms on Earth -bacteria - did not evolve into multi cellular forms.

Some dimensions of an organism may become simple while other dimensions may become more complex. It all depends on its way of life. Eg., the tapeworm has adaptations that enable it to avoid the immune system of the human body. The minimal definition of evolution as given in this post is:

Evolution is a process that results in heritable changes in a population spread over many generations.

As Susan Blackmore says in this TED talk, (variation + selection + heredity) MUST result in evolution. The organism shaped by evolution is not the perfect, but the good-enough. It is not striving for anything. It just depends on the differential survival and reproduction of replicating units that have high copying fidelity with occasional errors. It is incredible to think that fungi and giraffe are different manifestations of the same simple process. When I first had a clear grasp of this idea., I had a similar reaction to what Keats had when he read Chapman's Homer.

The term 'survival of the fittest' appears in the chapter but is not explained. This is a much misunderstood term. The word 'fittest' is taken to mean 'strongest' and is often used to justify the Gordon Gekko-style 'greed is good' philosophy. Actually it just refers to an organism that best ' fits' its environment. A pusillanimous rabbit that takes flight at the slightest sign of danger is fitter than an intrepid rabbit that investigates every suspicious sound. The former will leave descendants while the latter will be lunch.

About speciation, the textbook says:

Thus speciation is arising of a new species from a sub-population of a species which is geographically or reproductively isolated over a long period of time from the other population of the same species.

The 'or' is confusing here.Though defininga species is not easy, speciation just means the evolution of different groups through reproductive isolation over a long period of time so that there is no gene flow between the two groups. These genetic differences gradually grow larger to the extent that the individuals of the two groups cannot interbreed. The most common way in which reproductive isolation occurs is by geographical isolation, a process known as allopatric speciation.

While discussing the formation of new species,it is mentioned at one point: "Then they would be ready to become two different species." This is not how evolution happens. It is not as if the best and the brightest of a species held a conference , decided that that they have had enough of this practice business and that it is time for them to become new species. There is no conscious strategy involved. The language of conscious strategising is often used but that is only for expository convenience.

What actually happens is that because of the variation of individuals in a population, some individuals will have certain characters (morphological, anatomical, physiological or behavioral) that will give them an advantage over individuals that don't have them.Thus more of these individuals will survive and reproduce on average and leave copies of their genes to future generations. By this process, that particular character becomes more common in that species over many generations.

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About Me

I am an Engineer/MBA forced into early retirement. In 1999, at the age of 32, I suffered a brain stem stroke which left me a quadriplegic without speech. This blog is mainly about my life after the stroke.